During the maintenance of naltrexone narcotic blockade in postaddicts, some patients may at times use non-narcotic abuse drugs, such as cocaine, barbiturates, amphetamine, etc., as well as alcohol. Animal studies are being undertaken to determine if the simultaneous use of these various non-narcotic abuse drugs would affect either the efficacy or safety of oral naltrexone administered to animals. This is being done by determining the effect of various abuse drugs on (a) the potency of oral naltrexone in blocking the Straub tail in mice and the loss of righting reflex in rats after morphine administration, and (b) the toxicity of naltrexone. Studies are also being done to determine what drugs may counteract toxic doses of naltrexone, so as to develop potential antidotes for possible use in the event that overdosage in man ever occurs.